Brain-specific proteins are being looked for by comparing two- dimensional (DEAE-cellulose x acrylamide gel electrophoresis) "protein maps" for brain proteins to those from liver and other organs. Then the proteins are purified, antiserum prepared, and using a C'-fixation assay, the presence of the protein in brains of different species is tested, the protein is assayed in areas of brain, localized in cell- type, and levels studied during development and degeneration. Two proteins, S-100 and 14-3-2, have been put through these procedures and at least four others are currently being investigated.